Shipley and Felicetti’s study (2002) on the small blue duiker species of antelope concluded that the duiker’s digestibility was higher than that of larger antelope species. So, this raised the question of whether all smaller antelope species have greater digestibility than that of larger antelope species. The greater kudu and the lesser kudu are two sympatric species of antelopes found in Africa that greatly differ in size, but are physiologically and anatomically similar. Thus, their digestibility could be tested to establish if there is a difference in digestibility related to size among closely related antelope species.
To determine if digestibility changes with body size among antelopes, we will conduct a series of digestion trials on diets ranging in fiber, proteins, and tannins. This study will help us understand the greater and lesser kudu’s energy and protein requirements and their tolerance for fiber and tannins. This knowledge will assist in conserving these animals in their natural environment and determining their proper diets in zoos.
Tannins are found
Methods
For our digestion experiments we will use three adult male greater kudu and three adult male lesser kudu that have been born in the wild. The animals will be kept in indoor/outdoor pens for three months before the experiments to standardize their conditions. The animals will be fed a maintenance diet of pelleted ruminant ration that was formulated by Washington State University for the Shipley and Felicetti study (2002), natural browse, raisins, and apples, with a trace mineral block from Morton International, Inc. in Chicago, Illinois. They will be provided with tap water, as the antelope need it.
During feeding trials, both species will be offered a fresh diet each day of some food containing tannins and some not containing tannins. We will use the same diet fed to the blue duikers in the Shipley and Felicetti (2002) study. As seen in table 1, alfafa (Medicago sativa), apples (Macintosh variety; Malus sp.), dried black mission figs (Ficus carica), a pelleted ruminant ration, and smooth brome (Bromus inermis) contain tannins. And, English oak acorns (Quercus robur), Pacific willow leaves (Salix lasiandra), poplar leaves (a hybrid of Populus trichocarpa and P. deltoids), and fireweed (Epilobium angustifolium) do not contain tannins (Shipley and Felicetti, 2002). An African diet is unnecessary in this study since the specific fiber, nitrogen and BSA precipitate has already been established for the selected food items. These diets range five-fold in fiber content and ten-fold in nitrogen content (Table 1).
We will conduct five-day total collection trials following a ten-day pretrial similar to the way they did in the Shipley and Felicetti study (2002), during which animals will be moved from their indoor/outdoor facilities to indoor metabolic crates and given time to become accustomed to both the diet and their temporary housing. At the end of each trial, animals will be moved back to their maintenance facility and gradually fed their maintenance diet for at least 15 days. Animals will be weighed before and after each five-day collection. Mineral blocks will be provided, and food and water will be offered. Food will be weighed and fed to the greater and lesser kudu each morning of the trial. To ensure that the kudu ingest homogeneous diets, we will prepare the diets before feeding. Willow and poplar leaves will be stripped from the branches, apples with peels will be cored and cut into two cm. cubes, and acorns will be shelled. Alfalfa, fireweed, and smooth brome will be harvested to provide a diet of leaves and small stems, with no flowers or seed heads. Orts (scraps of food left after a meal is completed) will be collected, weighed and corrected for dry matter, and subtracted from the amount given the previous day to determine how much dry matter each animal ingests daily (DMI). Feces will fall onto mesh screens placed below the cages, and urine was will be funneled into bottles containing approximately five milliliters of 1 N Hydrochloric acid. We will dry samples of food, feces, and orts daily at 100 degrees Celsius for 24 hours to determine the dry matter content. Samples of food, feces, orts, and urine will be collected daily and stored at –20 degrees Celsius. At the end of a trial, each individual’s orts, feces, and urine will be pooled across the five-day trial. Food, feces, and orts will be dried at 50 degrees Celsius for four days, ground, and stored for later analysis of neutral detergent solubles (NDS), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), nitrogen, and energy content. Urine will be stored at –20 degrees Celsius and later analyzed for nitrogen content.
We will measure the gross energy of the feces using bomb calorimetry, following the procedure described in the AOAC’s “Official methods of analysis” (1984). The feces will be analyzed for fiber composition using sequential detergent analysis, using the methods of Goering and Van Soest (1970). Nitrogen content will be determined with Kjeldahl analysis, again following the procedure described in the AOAC’s “Official methods of analysis” (1984). The capacity of condensed and hydrolysable tannins to bind proteins in each forage was determined by the bovine serum albumin (BSA) method (Robbins et al., 1987a) in the Shipley and Felicetti study (2002). Diets that precipitated more than 0.015 milligram (mg.) BSA per mg dry forage (i.e., alfalfa, apples, figs, smooth brome, and pelleted ration) were considered nontannin diets (Robbins et al., 1987a; Robbins et al., 1987b; Felicetti et al., 2000) (Table 1). All other diets were considered tannin-containing diets.
The following components will be calculated as they were in the Shipley and Felicetti study (2002). Metabolic fecal nitrogen (MFN, g N/100 g feed) will be estimated as the negative y-intercept of the regression of digestible nitrogen (g nitrogen/100 g food) against dietary nitrogen (%). True nitrogen (%) will be estimated as the slope of the regression line. The y-intercept of the regression of urinary nitrogen (mg nitrogen/kg0.75/ day) against dietary nitrogen intake (mg nitrogen/kg0.75/day) will provide an estimate of endogenous urinary nitrogen (EUN, mg nitrogen/kg0.75/day). Minimum nitrogen requirements of the greater and lesser kudu (i.e., the amount of nitrogen an animal must ingest to counteract the minimum constant losses from feces and urine, mg nitrogen/kg0.75/day) will be estimated as the x-intercept of the regression of nitrogen balance (nitrogen ingested minus nitrogen excreted, mg nitrogen/kg0.75/day) against dietary nitrogen intake (mg nitrogen/kg0.75/day). Tannin diets will be omitted from these analyses because tannins artificially increase fecal nitrogen losses and decrease urinary losses (Robbins et al., 1987a). In addition, data from an animal will be omitted when calculating MFN and EUN if it loses more than 5 percent of its body mass during the trial because the lost body mass may include metabolized body protein, biasing estimates of MFN and EUN. Minimum dietary protein requirements will be derived from the equation [(EUN + MFN(DMI) * 6.25)/DMI/0.74] (Robbins, 1993). To examine the effects of tannins on protein digestion, we will calculate the residuals of all tannin and nontannin diets from the best-fit line of digestible nitrogen (g nitrogen/100 g feed) against dietary nitrogen (%). We will then conduct a linear regression of the residuals against a measure of the protein precipitating capacity of the tannins in the diets (i.e., BSA precipitation, mg/mg forage dry matter [Robbins et al., 1987a]) that were calculated in the Shipley and Felicetti study (2002). We will determine the dry matter digestibility for each of the kudu by using the equation [(g forage/day – g feces/day)/(g forage/day)].
Next, we will compare the results of the greater kudu and the lesser kudu to see if size does affect the digestibility of the antelopes. While this data should show whether or not the smaller lesser kudu has a higher rate of digestibility than the larger greater kudu, it does not show whether it is true for all antelopes (or even other types of animals) or why it is true. So, further studies could be done on other species of antelopes and other types of animals to see if the trend is true for them. Other studies could be done on the anatomical features of the greater and lesser kudu to determine if an anatomical difference accounts for the difference in digestibility. The data provided in this study could also be given to zoos holding the greater and lesser kudu to determine whether the diets they are being fed meet their requirements.
TABLE 1a. Nutritional content of forages fed to lesser and greater kudu
aFrom the Shipley and Felicetti study (2002)
bDiets considered “tannin-containing” in analyses
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